Question

In biology, we say that "Every Gene Codes for One Protein". But we've learned that this is
not absolutely true. We estimate that there are about 30,000 genes in humans, but
there are actually probably hundreds of thousands of proteins made from those genes.
What mechanism that we've learned about in class is probably responsible for creating
all these different proteins? Explain how this mechanism would work to create two
different proteins from the same gene.

Answer 1

Answer:

Two different proteins can be produced from a single gene by the following mechanisms:

1. Transcriptional Mechanism - Presence of multiple transcription initiation sites in the gene.
2. Post-transcriptional Mechanism - Generation of multiple transcripts from a single messenger RNA (mRNA) by the method of alternative splicing.
3. Translational Mechanism - Presence of multiple start codons in the mature mRNA transcript, giving rise to multiple proteins.
4. Post-translational Mechanism - The protein produced from the mature mRNA transcript can undergo chemical modifications.

Explanation:

• The gene can have multiple transcription initiation sites. When transcription starts from either of the transcription initiation sites it will give rise to different mRNA transcripts, that in turn, will gives rise to different proteins.
• Splicing is the method by which the intron sequences are removed from the precursor mRNA molecules and the exons are linked together to give rise to mature primary mRNA transcripts.
• Alternative splicing is the method involving the differential removal of introns from the precursor mRNA (depending upon the need) resulting in the generation of multiple mature mRNA transcripts that in turn can give rise to multiple proteins.
• Presence of multiple translational start codons in the mature mRNA transcript allows the differential translation of multiple proteins, by the ribosome, from each start codon.
• Proteins produced by translation from the mature mRNA transcript can undergo chemical modifications like glycosylation, methylation or lipidation with each having different functions.